You will need a valid passport (see guide lines here) and a credit card (Master or Visa).
Applicants need to visit the official government website www.evisa.gov.tr and purchase an e-visa online.
Please follow the online step-by-step process from the e-visa website.
Applicants need to print out their e-Visa and show it to customs officials when entering Turkey.
Prices are approx. 12GBP or 20USD
There are a number of unofficial websites offering 'e-visa' stickers, however, these are not official and not endorsed by the Turkish government. It is advisable that you do not use these websites.
Please note: Turkish authorities can deny entrance of a holder of e-Visa to Turkey in certain cases. Holders of visas issued by Turkish embassies or consulates are subject to the same procedure too, thus can be denied entrance.